2 Epidemiology of low back pain M.L.

SKOVRON

This chapter summarizes the available evidence from a number of representative studies published in Europe and North America regarding the epidemiology of acute and chronic low back pain. It addresses the burden of back pain in the adult population in industrialized countries; and individual, life-style and occupational risk factors. While the number of epidemiologic studies of back pain is quite substantial, estimates of the frequency and impact of back pain vary. This is at least in part because of varying sources of information and definitions of back pain used in different studies. In addition, the medical care and insurance systems of the different countries may influence the extent to which episodes of back pain are reported, brought to medical attention, or result in absence from work. While information on several risk factors is well-established, for some the evidence is insufficient or contradictory. This is partly because of limitations in the designs of most studies conducted to date. For example, in addition to problems of information sources and definitions, most risk factor or causal studies of back pain are cross-sectional. Such studies yield prevalence data, the proportion of subjects who currently have (point prevalence), have had over a period of time (period prevalence), or have ever had (life-time prevalence) the condition in question (in this case back pain). Prevalence data are useful for estimating the magnitude of the problem and the demand on health services but are not as useful for testing hypotheses about causality. This is for several reasons. Prevalence data are biased by selective attrition. Cases with the longest duration tend to be over-represented in prevalence data, so that associated risk factors may be more closely related to duration than to the risk of occurrence of any episode. The time of exposure to the hypothesized risk factor relative to the time of onset of the back pain cannot be easily determined from a crosssectional study. It is often not possible to determine from cross-sectional studies whether the hypothesized causal factor preceded the onset of back pain in time. The more robust type of study for hypotheses regarding causality is the cohort, prospective or longitudinal study. In this type of study the determination of exposure to a causal factor is made before onset of disease. Study subjects are followed over time and new (incident) cases are identified. The resulting incidence rates (frequency of new episodes in Bailli~re' s Clinical Rheumatology--

Vol. 6, No. 3, October1992 ISBN0-7020-1637-3

559 Copyright9 1992,byBailli6reTindall Allrightsofreproductionin anyformreserved

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the population per unit time) provide stronger evidence for causal hypotheses than the results of cross-sectional studies, as the time sequence of events is clearly established and the duration of morbidity does not influence the probability of identification of cases. A further limitation of the available literature on the epidemiology of simple low back pain is conceptual. Investigators from different disciplines have viewed the problem from their own perspective, leading to investigations focusing, for example, on biomechanical factors without attention to other factors which could influence in different ways onset of pain, reporting of pain, disability and duration. While the complex nature of disability due to low back pain has been recognized for some time (Wood, 1980), few studies have been designed either to test adequately the relative importance of biomedical, mechanical and psychosocial factors in onset and duration of back pain, or to elaborate the interrelationships among risk factors. The

RISKFACTORS

OUTCOMES

Occupational: Workorganisation~ Position [ Lifting [ Vibration ) Individual: " -,Physical -,Psychological -->Life-style

i= Load

[

~

=, Sprain-Strain

.~~Abs!nce

MedicalVisit Figure 1. Possiblerelationshipsamongrisk factorsand low back pain.

PREDICTORS: INDIVIDUAL: OCCUPATIONAL: Physical ] Load~Jobsatisfaction Psychological| ~ Workorganisation Life-style ~ ' \ ~ ~ /

.,sto

/

SOCIAL: [" Education ,~ Income /L socialsupport

\CLINICAL MANIFESTATION:J --History / --Severity /

OUTCOMES:

Recovery--Disability (functionaland/ororganic)

Figure 2, Possiblerelationshipsamongpredictorsand outcomein low back pain.

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561

evidence regarding risk factors for low back pain is still formulated in 'laundry lists', perhaps categorized as to type of factor, with as yet little attention to the complex web of causality which these risk factors represent. This chapter, of necessity, proceeds through a linear presentation of information regarding predictors of tow back pain and chronicity. The reader may wish to conceptualize the problem in the light of the suggested models in Figures 1 and 2, which illustrate relationships among factors potentially responsible for onset and chronicity in low back pain. FREQUENCY, MEDICAL CARE UTILIZATION, COSTS Low back pain is a frequent cause of activity limitation in adults in industrialized countries. By middle life, it is usual to have experienced an episode of low back pain. For example, investigators in Denmark (Biering-Sorensen, 1983a), Sweden (Hult, 1954; Svensson, 1982; Svensson and Andersson, 1983), the USA (Frymoyer et al, 1980) and the Netherlands (Valkenburg and Haanen, 1982) have reported, based on cross-sectional studies, that 50-70% of adults report having experienced low back pain at some time in the past. As many as 25% of adults report experiencing back pain in a given year (Haber, 1971; Gyntelberg, 1974). The experience of back pain does not necessarily lead to absence from work. Biering-Sorensen (1983b) reported that, although approximately 70% of the subjects studied had at one time experienced low back pain, only 23% of these reported that they had ever stayed home from work. From these data the life-time prevalence of sickness absence due to low back pain can be estimated to be 15-18%. Indeed, sickness absence due to compensable low back pain occurs in 1-2% of workers in the USA, Canada and the U K (Benn and Wood, 1975; Spitzer et al, 1987; National Safety Council, 1991). There is evidence that the problem of work loss due to low back pain is increasing. In Sweden, it is estimated that the annual frequency of sick-listing due to low back pain increased from 1% in 1970 to 8% in 1987 (Nachemson cited in Andersson, 1991). This increas/eoceg~ed while overall reports of back pain continued at 20-25% per year. Back pain leads to a substantial demand for medical care. In the USA, back pain was the second most common reason for physician visits in 1977-78, accounting for 2.3 % of all visits (Cypress, 1983), with an estimated 2.8 physician visits per episode (Kramer et al, 1983). Benn and Wood (1975) estimate 20/1000 general practice visits, 9/1000 referrals, 1/1000 hospital admissions, 0.1/1000 surgeries, 2/1000 handicapped-pensions and 7/1000 with spinal symptoms. The average duration of hospitalization was 10 days in the early 1980's, with annual medical costs for treatment of back pain totalling one billion dollars (Grazier et al, 1985). Biering-Sorensen (1983b), in his study in Denmark, reported that 60% of those with low back pain had consulted a general practitioner, 25% a specialist, and 15% a chiropractor. In the USA a similar pattern has been observed. Deyo and Tsui-Wu (1987), based on a national sample in the USA, estimated that 14% of adults have had back pain of at least 2 weeks'

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duration, with 10% reporting having experienced an episode in the previous year. Of low back pain sufferers, 85% (or 12% of the population in this study) had sought care from a health professional. The general practitioner was the most commonly consulted (59%), followed by orthopaedists (37%) and chiropractors (31%). Of those in the back pain group, 31% were hospitalized and 12% had surgery. In the UK, various studies have estimated that the annual rate of medical visits to general practitioners is 20-25 per 1000 population (Dillane et al, 1966; Barker, 1977). Wood and Baddeley (1980) estimate that in the UK new episodes of back pain led to 75 medical visits per general practitioner in the National Health Service annually, 609 per orthopaedist, 279 per osteopath and 368 per chiropractor. Total annual visits per practitioner were 140, 2394, 2735 and 5309 respectively. Examination of these data suggest that in Britain the largest number of visits per case occurs in chiropractic. In the Netherlands, where 51% of men and 58% of women studied reported a history of low back pain, 28% of men and 42% of women had consulted a physician due to low back pain (Valkenburg and Haanen, 1982), with 3.5 % of males and 6.3 % of females being treated for a rheumatological complaint including low back pain at the time of the survey. The cross-national differences in patterns of medical care reflect, at least in part, differences in organization of care. For example, in the USA, Canada, and the UK, low back pain is usually first seen by a primary care physician and then referred to an orthopaedist; while in the Netherlands, referral is to a rheumatologist. NATURAL HISTORY

While low back pain is frequent, it is largely self-limiting. In Canada, 75% of compensable back pain resolves within 4 weeks and 90% within 3 months. In 5% of cases, back pain persists for 6 months or more (Spitzer et al, 1987). These figures are relatively invariant across several countries (Andersson et al, 1983; Grazier et al, 1985). The average duration of lost-work episodes due to back pain has been reported as 30 days in the UK (Wood and Baddeley, 1980) and 23.5 days in the USA (Andersson, 1991). The prevalence of 'chronic' back pain, usually defined as back pain of more than 6 months duration varies: 1% in the USA, 0.05% in the UK, 4% in Finland (Klaukka et al, 1982), and 4% in Sweden (Svensson and Andersson, 1983). Although the proportion of back pain episodes leading to long-term disability is relatively small, recurrence is common. Nachemson, in Sweden, has estimated that the frequency of recurrent episodes of low back pain is about 60% over a 2-year period (Nachemson cited in Andersson, 1991). In Canada, the recurrence rate for compensable episodes was 36% over 3 years (Abenhaim and Suissa, 1987). In the Netherlands, 83% of subjects with a history of low back pain have had more than one episode (Valkenburg and Haanen, 1982). Presenting symptoms are predictive of the natural history of low back

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pain. In particular, the presence of sciatic symptoms is associated with both a longer duration of the episode (Wood and Baddeley, 1980), and severity of the episode (Damkot et al, 1984). INDIVIDUAL CHARACTERISTICS AND LOW BACK PAIN Low back pain is a condition of early onset. The highest age-specific incidence rate is in the early 20's with a gradual decline in later years. Prevalence of low back pain increases with age until the 60's (Biering-Sorensen, 1983a; Deyo and Tsui-Wu, 1987). The reasons for the decline in reported history of low back pain in older people are not clear, although it has been suggested that back pain becomes less important to respondents as other health problems of ageing occur and is then less fikely to be reported (Deyo and Tsui-Wu, 1987). Males

Females

1009080o

S

7060-

50~ 40-

o 302010q

30

40

50 Age

60 30

40

50

60

Age

Figure 3. Age-specific incidence and prevalence of low back pain by gender. - - , life-time prevalence;---, 0ne-year incidence. Adapted from Biering-SCrensen(1984).

The age-specific incidence and prevalence rates of work absence related to back pain follow the pattern of back pain in general, but at lower levels as expected (Klein et al, 1984; Lloyd et al, 1986; Spitzer et al, 1987). As the prevalence of back pain history-increases with age, so does the duration of back pain episodes and risk of chronicity (Troup et al, 1987; Deyo and Bass, 1989; Gallagher et al, 1989; Lacroix et al, 1990; Burton and Tillotson, 1991; Volinn et al, 1991). The overall prevalence of reported back pain is similar for males and females (Biering-Sorensen, 1983a; Lee et al, 1985; Deyo and Tsui-Wu, 1987). History of previous pregnancy is a risk factor for back pain in women (Svensson et al, 1990; Ostgaard et al, 1991). Although women experience

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back pain as commonly as men, their rates of sickness absence and compensable injuries due to back pain are generally lower (Klein et al, 1984; Spitzer et al, 1987), probably because women are not usually employed in occupations at high risk for back injury. While in men the pattern of declining incidence of sickness absence due to back pain after the 20's and 30's is well established, there is a suggestion that the pattern in women is not as marked (Biering-Sorensen, 1983a; Spitzer et al, 1987). In at least one population-based study of people 65 years of age and older, women reported a higher prevalence of recent back pain than men (Lavsky-Shulan et al, 1985). It has been suggested that this reflects the onset of vertebral fractures associated with postmenopausal osteoporosis (Deyo and Tsui-Wu, 1987). There is sparse evidence regarding the relationship of gender and the natural history of low back pain, although the data on railroad workers of Sander and Meyers (1986) suggest that women have longer durations for on-the-job injury and shorter durations for off-duty injuries than do men. Although some cross-sectional studies have suggested that height and weight are risk factors for low back pain, this has not been substantiated by most studies (Hult, 1954; Hirsch et al, 1969; Horal, 1969; Pope et al, 1985). In the Boeing prospective study of Boeing aircraft workers, it was found that there were no anthropometric factors predictive of first-time work absence due to low back pain in aircraft workers. However, in subjects with a prior history, substantial obesity in women and height in men was predictive of a subsequent episode (Battie et al, 1990). Height has been linked to risk of herniated disk in other studies (Rowe, 1969; Kelsey and Hardy, 1975; Heliovaara et al, 1991). Similarly, leg length inequality, although suggested in some studies, has not been reliably associated with low back pain (Hult, 1954; Pope et al, 1985; Soukka et al, 1991). A number of studies have reported that trunk muscle strength is reduced in patients with low back pain (Pederson et al, 1975; Berkson et al, 1977; Hasue et al, 1980). However, they all suffer from the possibility that the reduction in strength was consequent to the back pain. In the prospective study of Boeing aircraft workers (Battie et al, 1989a), isometric trunk strength was not predictive of subsequent back injury. It has been suggested that the contradictory results of these studies may be attributable to technical problems in measurement of static strength. Consequently, further research in the role of dynamic strength is underway at a number of centres. Mostardi et al (1991) have recently reported that isokinetic lifting strength is not predictive of back injury in a prospective study of nurses. However, this study lacked statistical power for an adequate test of the association. Further studies of larger numbers of subjects are needed. Spinal range of motion, particularly flexion, is reduced in patients with back pain (Pope et al, 1980). However, this may also be consequent to low back pain, as Battie et al (1990) found that no indicators of spinal flexibility predicted subsequent back injury. Reduced flexibility, however, may predict recurrence of back pain (Biering-Sorensen, 1984) and duration of episodes (Troup et al, 1987; Burton and Tillotson, 1991) even when controlling for other factors. Physical fitness and aerobic conditioning have been found in a prospective

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EPIDEMIOLOGY OF LOW BACK PAIN Table 1. Individual risk factors for low back pain and chronicity. Onset

Chronicity

Biological Age Cardiovascular fitness +

Age Spinal flexibility +

Cigarette smoking Pregnancy in women

Cigarette smoking +

Life-style

study to be protective against subsequent back injury in a cohort of firefighters who perform heavy work (Cady et al, 1979). However, where physical requirements of work are not great, aerobic capacity was not associated with subsequent back injury (Battie et al, 1989a,b). LIFE-STYLE AND LOW BACK PAIN Among life-style factors, cigarette smoking has been associated with low back pain and particularly with herniated disc in a number of studies (Gyntelberg, 1974; Frymoyer et al, 1983; Kelsey et al, 1984a). However, this association has not yet been reported in prospective studies and may not in fact be causal. At present, it is also not known whether cigarette smoking is related to duration or recurrence of back pain episodes, although the results of the study by Deyo and Bass (1989) suggest that this is so. Chronic back pain patients have been found to have greater alcohol consumption than healthy subjects or acute patients (Sandstrom et al, 1984; Vallfors, 1985). Comparing the pain drawings of back pain patients, Bergenudd and Johnell (1991) reported that men with somatic drawings had higher serum "y-glutamyltransferase levels, indicating consumption of alcohol and/or pain killers, than did men with non-somatic pain drawings. This association may represent a change in behaviour occurring as the period of low back disability is extended rather than a risk factor for onset of low back pain. Prospective studies are needed to evaluate the time sequence of the relationship between alcoholism and back pain chronicity. PSYCHOSOCIAL FACTORS AND LOW BACK PAIN Psychological distress has long been associated with chronic back pain (Love and Peck, 1987; Lacroix et al, 1990). The patient's perception of disability and fear of activity have also been related to chronicity of back pain patients (Waddell et al, 1984; Sandstrom and Esbjornsson, 1986; Hazard et al, 1991). Psychosocial factors have been associated with reporting of back pain as well (Mechanic and Angel, 1987). Low job satisfaction has been suggested as associated with sickness absence due to low back pain (Dehlin and Berg, 1977; Bergenudd and Nilsson, 1988) and with somatic versus non-somatic pain drawings (Bergenudd and Johnell, 1991). Recently, in prospective

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studies of Boeing aircraft workers, elevated scores on the hysteria subscale of MMPI were found to be predictive of subsequent disabling back injury. In this investigation, the employee's job satisfaction was found to be an even stronger predictor of subsequent injury (Bigos et al, 1991). An earlier retrospective report on the same population indicates that a poor performance rating by supervisors was also associated with work absence due to back pain (Bigos et al, 1986). The relative importance of these psychosocial factors and physical demands of work were not analysed in these studies. This question requires further investigation. Socioeconomic factors such as divorced or widowed marital status (Gyntelberg, 1974) and low educational attainment (Deyo and Tsui-Wu, 1987; Bergenudd and Nilsson, 1988) have been suggested as related to reported back pain or occupational back injury in cross-sectional studies. These associations may operate through other factors; for instance, through the association of educational attainment with physical requirements of work. Studies reported to date have not been designed to evaluate the relative importance of psychosocial and job-related factors in risk of back pain. The availability of wage replacement has been implicated in incidence and duration of work absence due to back injuries (Walsh and Dumitru, 1988; Hadler, 1989). The fndings of Sander and Meyers (1986) that railway workers with on-duty back injury were off duty substantially longer than those injured off duty, for similar age of employee type and severity of injury are consistent with this suggestion. An analysis of time trends in workers' compensation claims in the USA found that as compensation increased beyond the rate of inflation, there was a concomitant increase in incidence and duration of claims for unverifiable pain or strain, which were predominantly back injuries (Robertson and Keeve, 1983). Volinn et al (1991), however, analysing workers' compensation claims in Oregon, did not find that workers' compensation exceeding wages was associated with the duration of time lost due to compensatable back injuries. Cats-Baril and Frymoyer (1991) found that characteristics such as job satisfaction, the perception of fault, past hospitalizations and education were predictive of chronicity in a series of patients enrolled during the first 3 months of their initial episode of low back pain. Clinical (physical and personality) characteristics of the patients were not predictive. In a study of a mixed population of back pain patients, Gallagher et al (1989) did report that the MMPI hysteria score predicted chronicity, as did health locus of control, when age and duration of prior work absence were controlled.

OCCUPATION AND LOW BACK PAIN Manual materials handling Occupational risk factors for back injury include manual materials handling, particularly heavy lifting (Magora, 1972; Chaffin and Park, 1973; Biering-

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Sorensen, 1983b; Damkot et al, 1984; Riihimaki, 1985; Skovron et al, 1987a; Venning et al, 1987; Burton et al, 1989) and lifting while twisting (Kelsey et al, 1984b). In a study examining workers' compensation data in 26 states, incidence rates for compensatable back injury were highest in occupations requiring heavy lifting, such as miscellaneous labourers, trash collectors, lumbering, nursing aides and Licensed Practical Nurses (Klein et al, 1984): Reviewing published epidemiologic and biomechanical studies, Kelsey and Golden have found that there appears to be a threshold in the relationship of lifting requirements and back injury, with an increased risk of injury occurring in jobs requiring frequent lifting of objects weighing 25 pounds or more (Kelsey and Golden, 1988). Punnett et al (1991), in a study of automobile workers, found that lifting loads in asymmetric postures increased the load on the spine and that lifts exceeding 40 N increased the risk of back injury. In a recent study, rated job requirements for strength and endurance were positively correlated with the incidence rate of lost-work back injuries in municipal transit workers (Skovron et al, 1991). The earlier described finding that trunk strength was not a risk factor for subsequent back injury in the prospective study of aircraft workers may reflect the relatively moderate physical demands of work in that cohort. In a prospective study of nursing personnel, Skovron et al (1987b) found that the perception of heaviness of work was associated with lost-work back injury. Chaffin and Park (1973), in a small prospective study, observed that when the physical requirements of work exceeded the subject's lifting strength, the risk of subsequent back injury was greater. These results have been confirmed in part in a multivariate analysis of a cross-sectional study by Troup et al (1987). Keyserling et al (1980) have suggested that exclusion from job placement of workers whose physical capacities are exceeded by job demands can lead to a reduction in back injuries. However, the study supporting this recommendation is a small one and remains to be confirmed on a larger scale. The perception of heaviness of work has been associated with chronicity (Troup et al, 1987; Burton and Tillotson, 1991). The work of Cats-Baril and Frymoyer (1991) and Goertz (1990) suggest that the job factors related to chronicity have more to do with job satisfaction and availability of alternative placements. These results remain to be confirmed.

Static postures Prolonged sitting postures at work have been associated with increases in low back pain in some studies (Hult, 1954; Magora, 1972), although this has not been confirmed by others (Svensson and Andersson, 1983). Nachemson and Elfstrom (1970) have reported that poorly designed seating induces loads on the spine similar to those associated with lifting in flexed positions, suggesting a possible biological mechanism for the association of back pain with prolonged sitting. In addition, asymmetric postures increase loads on the spine (Punnett et al, 1991) and are associated with increased risk of low back pain.

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Whole-body vibration

Occupational groups exposed to whole-body vibration, such as tractor, truck and bus drivers are also at increased risk of low back pain, particularly disk herniation (Gruber, 1974; Kelsey and Hardy, 1975; Gruber and Ziperman, 1976; Frymoyer et al, 1980; Kelsey et al, 1984a; Heliovaara, 1987; Burdorf and Zondervan, 1990). Pope et al (1991) have suggested that vehicle operators are exposed to vibration at the spine's resonant frequency, which may be responsible for the increased frequency of back complaints; particularly disk herniations in such occupational groups. It is possible that vibration also leads to fatigue of the paraspinal muscles so that they are more easily strained in jobs also requiring heavy lifting (Pope et al, 1991). Table 2. Occupational risk factors for low back pain and chronicity. Onset

Chronicity

Heavy work Repeated lifting Lifting while twisting Whole-body vibration Static postures Job satisfaction +

Lack of alternative placement Job satisfaction +

SUMMARY

At present, although there have been many epidemiological studies of risk factors for low back pain, there are few risk factors established in prospective studies; and our understanding of them remains relatively crude. Individuals in jobs requiring manual materials handling, particularly repeated heavy lifting and lifting while twisting, are at increased risk of back pain leading to work absence. In addition, exposure to whole-body vibration and job requirements for static postures are associated with back pain. Individual trunk strength has not been consistently demonstrated as associated with back pain; although there is some suggestion that when work requirements for heavy lifting exceed individual capacities, back pain is more likely to occur. The pattern of peak age at onset in the 20's is consistent with back pain development early in working life. Among other individual characteristics, only cigarette smoking has consistently been associated with back pain; and the biological mechanism for this finding is not understood. Evidence with respect to spinal flexibility, aerobic capacity, educational attainment and other variables is suggestive but not consistent. There is some evidence that the individual's relation to work, expressed as job satisfaction or supervisor rating, is also related to work absence due to back pain. While it is possible to describe, however crudely, the characteristics placing people at risk for back pain leading to work absence and/or medical attention, the problem of predicting chronicity and thus identifying patients

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for m o r e i n t e n s i v e clinical i n t e r v e n t i o n r e m a i n s u n r e s o l v e d . A t this t i m e , o n l y age of t h e p a t i e n t a n d c e r t a i n clinical f e a t u r e s of the b a c k p a i n such as t h e p r e s e n c e of sciatic s y m p t o m s , d u r a t i o n of the c u r r e n t e p i s o d e , a n d h i s t o r y of p r i o r e p i s o d e s a r e c o n s i s t e n t l y d e m o n s t r a t e d p r e d i c t o r s . I n c h r o n i c p a t i e n t s , t h e r e is suggestive e v i d e n c e t h a t spinal flexibility, t r u n k s t r e n g t h , a n d c e r t a i n p s y c h o l o g i c a l characteristics such as c o p i n g skills, f e a r a n d a v o i d a n c e of p a i n o r m o v e m e n t , j o b satisfaction, a t t r i b u t i o n of fault a n d h y s t e r i c a l o r h y p o c h o n d r i a c a l f e a t u r e s are a s s o c i a t e d with t r e a t m e n t failure. I n a d d i t i o n , t h e r e is suggestive e v i d e n c e that t h e availability of a l t e r n a t i v e w o r k p l a c e m e n t m a y allow for e a r l i e r r e t u r n to w o r k t h a n o t h e r w i s e . W h i l e t h e a v a i l a b i l i t y o f d i s a b i l i t y c o m p e n s a t i o n in excess o f usual w a g e s m a y serve as a d i s i n c e n t i v e to r e t u r n to w o r k . T h e l a t t e r - c i t e d r e m a i n to b e verified, while findings in c h r o n i c p a t i e n t s r e m a i n to b e t e s t e d in acute. F u r t h e r , t h e r o l e of p h y s i c a l d e m a n d s o f w o r k in d u r a t i o n o f b a c k p a i n e p i s o d e s has n o t b e e n well s t u d i e d .

Acknowledgement This work was partially supported by a grant from the National Institute for Occupational Safety and Health (CDC/NIOSH No. U60/CCU 206153-01).

REFERENCES Abenhaim L & Suissa S (1987) Importance and economic burden of occupational back pain: a study of 2500 cases representative of Quebec. Journal of Occupational Medicine 29" 670-674. Andersson GBJ (1991) The epidemiology of spinal disorders. In Frymoyer JW (ed.) The Adult Spine: Principles and Practice. New York: Raven Press. Andersson GBJ, Svensson HO & Oden A (1983) The intensity of work recovery in low back pain. Spine 8: 880-884. Barker ME (1977) Pain in the back and leg: a general practice survey. Rheumatology and Rehabilitation 16: 37-45. Battle MC, Bigos SJ, Fisher LD et al (1989a) Isometric lifting strength as a predictor of industrial back pain. Spine 14: 851. Battle MC, Bigos SJ, Fisher LD et al (1989b) A prospective study of the role of cardiovascular risk factors and fitness in industrial back complaints. Spine 14: 141. Battle MC, Bigos SJ, Fisher LD et al (1990) The role of spinal flexibility in back pain complaints within industry: a prospective study. Spine 15: 768-773. Battle MC, Bigos SJ, Fisher LE et al (19~90) Anthropometric and clinical measurements as predictors of industrial back pain complaints: a prospective study. Journal of Spinal Disorders 3: 195. Benn RT & Wood PH (1975) Pain in the back: an attempt to estimate the size of the problem. Rheumatology and Rehabilitation 14: 121-128. Bergenudd H & Johnell O (1991) Somatic versus nonsomatic shoulder and back pain experience in middle age in relation to body build, physical fitness, bone mineral content, gamma-glutamyltransferase, occupational workload, and psychosocial factors. Spine 16: 1051-1055.

570

M . L . SKOVRON

Bergenudd H & Nilsson B (1988) Back pain in middle age; occupational workload and psychologic factors: an epidemiologic survey. Spine 13: 58-60. Berkson M, Schultz A, Nachemson A & Andersson G (1977) Voluntary strengths of male adults with acute low back syndromes. Clincial Orthopaedics and Related Research 129: 84-95. Biering-Sorensen F (1983a) A prospective study of low back pain in general population. I. Occurrence, recurrence and etiology. Scandinavian Journal of Rehabilitative Medicine 15: 71-79. Biering-Sorensen F (1983b) A prospective study of low back pain in a general population. III. Medical service-work consequence. Scandinavian Journal of Rehabilitative Medicine 15: 89-96. Biering-Sorensen F (1984) A one-year prospective study of low back pain in a general population. Danish Medical Bulletin 31: 362-375. Bigos SJ, Spengler DM, Martin NA et al (1986) Back injuries in industry: a retrospective study: III. Employee-related factors. Spine 11: 252-255. Bigos SJ, Battie MC, Spengler DM et al (1991) A prospective study of work perceptions and psychosocial factors affecting the report of back injury. Spine 16: 1-6. Burdorf A & Zondervan H (1990) An epidemiological study of low-back pain in crane operators. Ergonomics 33(8): 981-987. Burton AK & Tillotson KM (1991) Prediction of the clinical course of low-back trouble using multivariable models. Spine 16(1): 7-14. Burton AK, Tillotson KM & Troup JDG (1989) Prediction of low-back trouble frequency in a working population. Spine 14: 939-946. Cady LS, Bischoff DP & O'Connell ER (1979) Strength and fitness and subsequent back injury in firefighters. Journal of Occupational Medicine 21: 269-272. Cats-Baril WL & Frymoyer JW (1991) Identifying patients at risk of becoming disabled because of low-back pain: the Vermont rehabilitation engineering center predictive model. Spine 16: 605-607. Chaffin DB & Park KS (1973) A longitudinal study of low-back pain as associated with occupational weight lifting factors. American Industrial Hygiene Association Journal 34: 513-524. Cypress BK (1983) Characteristics of physician visits for back symptoms: a national perspective. American Journal of Public Health 73: 389-395. Damkot DK, Pope MH, Lord J e t al (1984) The relationship between work history, work environment and low-back pain in men. Spine 9" 395-399. Dehlin O & Berg S (1977) Back symptoms and psychological perception of work. Scandinavian Journal of Rehabilitative Medicine 9: 61-65. Deyo RA & Bass JE (1989) Lifestyle and low-back pain. The influence of smoking and obesity. Spine 14(5): 501-506. Deyo RA & Tsui-Wu YJ (1987) Descriptive epidemiology of low-back pain and its related medical care in the United States. Spine 12: 264-268. Dillane JB, Fry J & Kalton G (1966) Acute back syndrome--a study from general practice. British Medical Journal 2: 82-84. Frymoyer JW, Pope MH & Costanza MC (1980) Epidemiologic studies of low back pain. Spine 5: 419-423. Frymoyer JW, Pope MH & Clements JH (1983) Risk factors in low back pain. An epidemiological survey. Journal of Bone and Joint Surgery 65: 213-218. Gallagher RM, Rauh V, Haurgh LD et al (1989) Determinants of return-to-work among low back pain patients. Pain 39: 55-67. Goertz MN (1990) Prognostic indicators for acute low-back pain. Spine 15: 1307-1310. Grazier K, Holbrook TL, Kelsey JL et al (1985) The Frequency of Occurrence, Impact, and Costs of Musculoskeletal Conditions in the United States. Chicago: American Academy of Orthopedic Surgeons. Gruber GJ (1974) Relationships between whole-body vibration and morbidity patterns among interstate truck drivers. US Department of Health Education and Welfare, DHEW (NIOSH) Publication No. 77. Gruber GJ & Ziperman HH (1976) Relationship between whole-body vibration and morbidity patterns among motor coach operators. US Department of Health Education and Welfare, DHEW (NIOSH) Publication No. 75.

EPIDEMIOLOGY OF LOW BACK PAIN

571

Gyntelberg F (1974) One-year incidence of lowback pain among male residents of Copenhagen aged 40-59. Danish Medical Bulletin 21: 30-36. Haber LD (1971) Disabling effects of chronic disease and impairment. Journal of Chronic Diseases 24: 469-487. Hadler N (1989) Disabling backache in France, Switzerland, and the Netherlands: contrasting sociopolitical constraints on clinical judgement. Journal of Occupational Medicine 31: 823-831. Hasue M & Fujiwara M (1980) Epidemiologic and clinical studies of long-term prognosis of low back pain and sciatica. Spine 4: 150-155. Hazard RG, Bendix A & Fenwick JW (1991) Disability exaggeration as a predictor of functional restoration outcomes for patients with chronic low-back pain. Spine 16: 1062-1067. Heliovaara M (1987) Occupation and risk of herniated lumbar disc or sciatica leading to hospitalization. Journal of Chronic Diseases 40: 259-264. Heliovaara M, Makela M, Knekt P e t al (1991) Determinants of sciatica and low-back pain. Spine 16: 608--614. Hirsch C, Johnson B & Lewin T (1969) Low-back symptoms in a Swedish female population. Clinical Orthopaedics and Related Research 63: 171-176. Horal J (1969) The clinical appearance of low back pain disorders in the city of Gothenberg, Sweden. Acta Orthopaedica Scandinavica 118 (Supplement). Hult L (1954) The Munkfors investigation. Acta Orthopaedica Scandinavica 16: 12-30. Kelsey JL & Hardy RJ (1975) Driving of motor vehicles as a risk factor for acute herniated lumbar intervertebral disc. American Journal of Epidemiology 102: 63-73. Kelsey JL & Golden AL (1988) Occupational and work place factors associated with low back pain. In Deyo R A (ed.) Back Pain in Workers; STARS 3: 7-16. Kelsey JL, Githens PB, O'Connor T et al (1984a) Acute prolapsed lumbar intervertebral disc: an epidemiotogic study with special reference to driving automobiles and cigarette smoking. Spine 9: 608. Kelsey JL, Githens PB, White A A et al (1984b) An epidemiologic study of lifting and twisting on the job and risk of acute prolapsed lumbar intervertebral disk. Journal of Orthopaedic Research 2: 61-66. Keyserling WM, Herrin GD & Chaffin DB (1980) Isometric strength testing as a means of controlling medical incidents on strenuous jobs. Journal of Occupational Medicine 22(5): 332-336. Klaukka T, Sievers K & Takala J (1982) Epidemiology of rheumatic diseases in Finland in 1964-76. Scandinavian Journal of Rheumatology (Supplement) 47: 5-13. Klein BP, Jensen RC & Sanderson LM (1984) Assessment of workers' compensation claims for back strains/sprains. Journal of Occupational Medicine 26: 443-448. Kramer JS, Yelin EH & Epstein WV (1983) Social and economic impacts of four musculoskeletal conditions. A study using national community-based data. Arthritis and Rheumatology 26: 901-907. Lacroix JM, Powell J, Lloyd GJ et al (1990) Low-back pain: factors of value in predicting outcome. Spine 15: 495-499. Lavsky-Shulan M, Wallace RB, Kohout FJ et al (1985) Prevalence and functional correlates of low back pain in the elderly: the Iowa 65+ rural health study. Journal of the American Geriatric Society 33: 23-28. Lee P, Helewa A, Smythe HA, Bombardier C & Goldsmith CH (1985) Epidemiology of musculoskeletal disorders (complaints) and related disability in Canada. Journal of Rheumatology 12: 1169-1173. Lloyd MH, Gauld S & Soutar CA (1986) Epidemiologic study of back pain in miners and office workers. Spine 11: 136-140. Love A & Peck C (1987) The MMPI and psychological factors in chronic low back pain: a review. Pain 28: 1-12. Magora A (1972) Investigation of the relation of low back pain and occupation. III: physical requirements: sitting, standing, and weightlifting. Industrial Medicine and Surgery 41: 5. Mechanic D & Angel RJ (1987) Some factors associated with the report and evaluation of back pain. Journal of Health of Social Behavior 28: 131-139. Mostardi RA, Noe DA, Kovacik MW & Porterfield JA (1991) Isokinetic lifting strength and occupational injury: a prospective study. Spine 17: 18%193. National Safety Council (1991) Accident Facts, 1991. Chicago.

572

M . L . SKOVRON

Ostgaard HC, Andersson GBJ & Karlsson K (1991) Prevalence of back pain in pregnancy. Spine 16: 549-552. Pederson OF, Peterson R & Staffeldt ES (1975) Back pain and isometric back muscle strength of workers in a Danish factory. Scandinavian Journal of Rehabilitative Medicine 7: 125128. Pope MH, Wilder DG & Frymoyer JW (1980) Vibration as an etiologic factor in low back pain. I Mec E Proceedings C121/B0: 43. Pope MH, Bevins T, Wilder DG et al (1985) The relationship between anthropometric, postural, muscular, and mobility characteristics of males, ages 18--55. Spine 10: 644. Pope MH, Anderson GBJ & Chaffin DB (1991) The workplace. In Pope MH et al (eds) Occupational Low Back Pain: Assessment, Treatment, and Prevention. St Louis: Mosby. Punnett L, Fine LJ & Keyserling WM (1991) Back disorders and non-neutral trunk positions of automobile assembly workers. Scandinavian Journal of Work, Environment and Health 17: 337-346. Riihimaki H (1985) Back pain and heavy physical work: a comparative study of concrete reinforcement workers and maintenance house painters. British Journal of Industrial Medicine 42: 226-232. Rowe ML (1969) Low back pain in industry. Journal of Occupational Medicine 11: 161. Sander R A & Meyers JE (1986) The relationship of disability to compensation status in railroad workers. Spine 11: 141-143. Sandstrom J & Esbjornsson E (1986) Return to work after rehabilitation. The significance of the patient's own prediction. Scandinavian Journal of Rehabilitative Medicine 18: 29. Sandstrom J, Andersson GBJ & Wallerstedt S (1984) The role of alcohol abuse in working disability in patients with low back pain. Scandinavian Journal of Rehabilitative Medicine 16: 147-149. Skovron ML, Mulvihill MN, Sterling RC et al (1987a) Work organization and low back pain in nursing personnel. Ergonomics 30: 359-366. Skovron ML, Nordin M, Sterling RC & Mulvihill MN (1987b) Patient care and low back injury in nursing personnel. Trends in Ergonomics~Human Factors'IV: 855-862. Skovron ML, Nordin MN, Halpern N, Hiebert R & Cohen H (1991) Do worker ratings of job-required physical abilities correlate with back injury rates? Proceedings, ISSLS 1991, Paris, France. Soukka A, Alaranta H, TaUroth K & Heliovaara M (1991) Leg-length inequality in people of working age: the association between mild inequality and low-back pain is questionable. Spine 16: 429-431. Spitzer WO, LeBlanc FE, Dupuis M et al (1987) Scientific approach to the assessment and management of activity-related spinal disorders: a monograph for clinicians. Report of the Quebec Task Force on Spinal Disorders. Spine 12(7S): 1-59. Svensson H-O (1982) Low back pain in forty to forty-seven year old men. If. Socio-economic factors and previous sickness absence. Scandinavian Journal of Rehabilitative Medicine 14: 55-60. Svensson H-O & Andersson GBJ (1983) Low back pain in 40- to 47-year old men: work history and work environment. Spine 8: 272-276. Svensson H-O, Vedin A, Wilhelmsson C et al (1983) Low-back pain in relation to other diseases and cardiovascular risk factors. Spine 8: 277-285. Svensson H-O, Andersson GBJ, Hagstad A et al (1990) The relationship of low-back pain to pregnancy and gynecologic factors. Spine 15: 371-375. Troup JDG, Foreman TK, Baxter CE & Brown D (1987) The perception of back pain andthe role of psychophysical testing of lifting capacity. Spine 12: 645. Valkenburg HA & Haanen HCM (1982) The epidemiology of low back pain. In White A A & Gordon SL (eds) Symposium on Idiopathic Low Back Pain, pp 9-22. St Louis: Mosby. Vallfors B (1985) Acute, subacute and chronic low back pain. Clinical symptoms, absenteeism and working environment. Scandinavian Journal of Rehabilitative Medicine 11: 5-98. Venning PJ, Walter SD & Stitt LW (1987) Personal and job-related factors as determinants of incidence of back injuries among nursing personnel. Journal of Occupational Medicine 29: 820-825. Volinn E, Van Koevering D & Loeser JD (1.991) Back sprain in industry. The role of socioeconomic factors in chronicity. Spine 16(5): 542-548.

EPIDEM1OLOGY OF LOW BACK PAIN

573

Waddell G, Main CJ, Morris EW et al (1984) Chronic low-back pain, psychologic distress, and illness behavior. Spine 9: 209-213. Walsh NE & Dumitrn D (1988) Financial compensation and recovery from low back pain. Occupational Medicine STARS 3: 109--122. Wood PHN (1980) Understanding back pain. In Jayson M (ed.) The Lumbar Spine and Back Pain, 2nd edn, pp 1-28. London: Pitman. Wood PHN & B addeley EM (1980) Epidemiology of back pain. In Jayson M (ed.) The Lumbar Spine and Back Pain, pp 1-15. London: Churchill Livingstone.